1. Field of the Invention
This invention relates to a disc reproduction apparatus, and more particularly, to magneto-optical disc units for reproducing information recorded on a magneto-optical disc.
2. Description of the Related Art
In a conventional magneto-optical disc unit, desired data can usually be recorded or reproduced based on a synchronization pattern recorded on a magneto-optical disc in predetermined cycles. That is, as shown in FIGS. 1A and 1B, the recording area of the magneto-optical disc is divided radially into sectors, each of which has a record of identification data ID (FIG. 1A) consisting of position information, such as recording track information and sector information, at the head and a record of desired data in the subsequent area.
A three-byte first synchronization pattern (SYNC) is recorded in this magneto-optical disc at the beginning and one-byte second synchronization patterns (RS) is recorded in this magneto-optical disc in predetermined cycles (or at intervals of tens of bytes), as shown in FIG. 1B. In this way, the magneto-optical disc unit effects what is called "byte synchronization" by finding the beginning of each single byte and fetching data in byte units based on this first synchronization patter (SYNC). Moreover, subsequent second synchronization patterns (RS) are detected in sequence based on this first synchronization pattern (SYNC), and the byte synchronization is corrected based on the result of detecting these second synchronization patterns (RS).
Thus, the byte synchronization difference is corrected based on the second synchronization pattern (RS), and desired data is recorded or reproduced without fail. For this, the magneto-optical disc unit generates a specified window signal based on the first synchronization pattern (SYNC) and selectively fetches a reproduction signal based on the window signal to obtain the second synchronization patterns (RS) in sequence.
When the second synchronization pattern (RS) is detected, the detection of errors in the second synchronization pattern due to a defect on the magneto-optical disc, etc., may be reduced if the window width of the window signal is narrowed and the recording density increased. However, once the window width is narrowed, occasions may arise in which the second synchronization pattern (RS) cannot be detected if time-axial fluctuation occurs in the reproduction signal due to jitter, etc.